System for studying electrical waves



June 2, 1953 A. LE R. OLSON SYSTEM FOR STUDYING'ELECTRICAL WAVES 2Sheets-Sheet 1 Filed May 16, 1951 Cdmm 22 8 59 3% \Rfioo E mm x 52 6moomT INVENTOR.

ALTON LEROY OLSON ATTORNEYS June 2, 19531 LE'R, QLSQN 2,640,927

SYSTEM FOR STUDYING ELECTRICAL WAVES Fi-led May 16, 1951 2 'Sheets-Sheet 2 33 *J' I -L l 54 53 56/}, INVENTOR- v I ALTON LEROY OLSONATTORNE Y5 Patented June 2, 1953 SYSTEM FOR STUDYING ELECTRICAL WAVESAlton Le Roy Olson, Hackensack, N. J., assignor to Allen B. Du MontLaboratories, Inc., Clifton, N. J a corporation of Delaware ApplicationMay 16, 1951, Serial No. 226,694

2 Claims. (01. 250 27) This invention relates to instruments forobserving repetitive electrical phenomena and particularly toinstruments for selecting one of a group of similar electrical impulsesand rendering it visible upon the face of a cathode ray tube.

It is frequently desirable to observe the waveform of a televisionsignal or the blanking or synchronizing portion thereof, and in order toclarify the observed pattern, only a small part of each televisionpicture signal, such as one line, is chosen for presentation. Means forselecting a particular line in each television picture signal forexhibition are disclosed in copending application Serial No. 37,342 byRalph P. Abbenhouse, now Patent No. 2,615,979. The present inventionutilizes one form of the method taught therein but accomplishes theresult with different, and generally less complex, circuits.

It is one object of this invention to provide a simplified and improvedselecting circuit for use with oscillographic measuring instruments.Other objects will be apparent after studying the followingspecification together with the drawings in which:

Figure l is a schematic diagram of the invention, and

Figure 2 shows typical waveforms of a television signal.

The components of the circuit shown are chosen particularly foroperation at the principal frequencies of the present day televisionstandards, 60 C. P. S., 30 C. P. S., and 15750 C. P. S. The invention isapplicable, however, to other standards, frequencies and uses, changesin components, therefore, being a mere matter of design for thoseskilled in the art.

In Figure 1 a source ll of television synchronizing impulses isconnected to an amplifier l2 having a gain control l3 in its outputcircuit. The gain control I3 is joined through an integrating circuit Mto a multivibrator Hi to enable the operatorto choose the odd-line orevenline field. The input circuit of a sawtooth wave voltage generatorI8 is connected to the output circuit of the multivibrator IE, and theoutput circuit of generator 18 in turn is connected to an oscillator l9comprising a pair of amplifier tubes 20 and 2| and including a delaycircuit 22 as an integral part thereof. A differentiating circuit 23connects the oscillator W to one input circuit of a coincidence gate, ormixer, circuit 24 having a source 25 of positive pulses with arepetition rate of 15,750 per second connected to a second input circuitthereof. Following the coincidence circuit 24 isja single-shotmultivibrator 26, comprising a continuous delay circuit 21, which isconnected through a differentiating circuit 28 to the synchronizingcircuit of an oscillograph 29. V

The operation of the'circuit in Figure 1 can best be explained withreference to'Figure 2, which shows typical television signal waveforms.The signal 3| generated by the source is a normal, compositesynchronizing signal, although a composite blanking signal 32 may beused, as well as a vertical blanking signal 33, synchronizing signal 34,or driving signal 36.

In the event that the composite synchronizing signal 3| or the compositeblanking signal 32 is supplied by generator II, it is necessary toseparate a vertical, or low frequency component from the remainder ofthe signal in orderto provide a triggering signal for the selectorcircuits. This is accomplished by means of the integrating circuit M,which transforms signal 3|, for instance, into signal 37.

The30 C. P. S. multivibrator I6 is triggered when signal 3] reachesvoltage level 38, but the circuit components of the multivibrator allowit to operate only every other field. If it happens that themultivibrator I6 starts off on the even field of the television signaland it is desired to examine thev signal corresponding to some line orlines in the odd field, it is only necessary to actuate the switch ofthe field selector circuit I! to cause the multivibrator Hi to change tothe odd field triggeia Circuit operates by supplying an additionalcharge to the 30 C. P. S. multivibrator I6 tocause it to skip a beat;and con-- sequently, the switch may be of the momentary contact,spring-return variety.

The multivibrator l6 provides a sharp voltage pulse 39 of sufficientamplitude to trigger the sawtooth-wave generator |8, which,.in thiscase, is of the high-vacuum type. The output voltage of the generator I8is shown as waveform 4| in Figure 2. Y

The oscillator I9 is very much like a multivibrator without feedbackcondensers. It is a bi-stable oscillator comprising two amplifier tubes20 and 2| of which tube 2| is normally conducting. When the sawtoothvoltage 4| reaches a level 42 tube 2|! starts tov conduct, dropping thevoltage level at the plate thereof and cutting off tube 2|, therebyfurther increasing the conduction of tube 20. 'Tube 20 continues toconduct as long as the voltage applied to the grid thereof exceeds level42, and when the voltage drops at the end of the sawtooth period, tube2| resumes conduction at time 43. The resultant 3 rectangular voltagewave 44 produced at the plate of the tube 2| has a duty cycle determinedby the setting of the resistors in the delay circuit 22.

It is one of the properties of this oscillator that the duty cycle isvariable over a wide range, limited only by the retrace time of thesawtooth wave. However,'since the repetition rate of the sawtooth, andhence of rectangular wave 43, is one-half the television frame rate, theline or lines which it is desired to observe may be chosen near thecenter of the duty cycle range; i. e., between 25% and 75%. The wideduty cycle range becomes important only when the whole selector circuitis operated at the same repetition rate as the signal to be'observed.

The properties of the oscillator most useful in the present mode ofoperation are in the provision of exact, stable clipping of acomparatively slowly varying voltage, together with great amplificationof the clipped voltage without having inherent time, or frequency,restrictions, The stability and freedom from time restrictions obtainmainly because of the absence of condensers in so-called time constantcircuits common to multivibrators, and the high amplification is theresult of the positive feedback used.

The rectangular wave 44 is difierentiated by circuit 23 t obtain thewave 46 having a, negative-going voltage spike 4T relatively fixed foreach cycle of wave 46. Spike 41 must occur within the flyback time ofthe sawtooth wave 4|. A positive-going spike voltage 43 is alsoproduced, and, as has been explained heretofore, this spike 48 isvariable over almost the entire period of the sawtooth wave 4|.

The Wave 46 is applied to one input circuit of the mixer tube 24comprising the suppressor grid, which is biased sufliciently negative toblock current through the tube 24 when the signal on the suppressor gridis below the level 49. The negative spike 4'! is thus effectivelyclipped off and only the positive spike voltage 48 has any effect on thetube 24. The spike voltage 48 may be chosen to have an amplitudesufficient to overload the suppressor grid enough to clip of! the top ofspike 48, although this is not absolutely necessary. The components inthe cir cuit 23 are chosen so as to differentiate the rectangular wave44 to produce spike voltage 48 which preferably has a duration less than4 of a second.

When the gate tube 24 is rendered conductive by the spike voltage 48. itis then in a condition to amplify one of the pulses from the source 25applied to the second input circuit comprising the cathode and controlgrid of tube 24. The source 25 might well be the source H and the outputsignal of source 25 would then be signal 3!. To show that source 25might be differentjust a source of horizontal driving pulses, forinstance, the output signal will be labelled am in Figure 2. If theduration of the spike 4:8 is sumciently short, it may be that nohorizontal synchronizing impulses from the source 25 will occurcoincidentally therewith,'but a small variation of the potentiometers inthe delay circuit 22 will cause the spike 48 to coincide with one of theimpulses 50. This impulse, and only this impulse, will be amplified bythe tube 24 once each television frame so that each 1&0 of a second anegative impulse 5! is applied to the multivibrator 26. By varying thepotentiometer in the delay circuit 22, different horizontalsynchronizing impulses may be chosen as pulse 5|. By operating the fieldselector circuit l'! the portion of a television frame that cannot becovered by complete variation of the potentiometer in the delay circuit22 may also be covered.

The multivibrator 28 has a continuous duty cycle control, or delaycontrol 21 to set the duty cycle of the rectangular output voltage 52.This output voltage is differentiated in the differentiating circuit 28to form a voltage 53 having a positive impulse 54 and a negative impulse56 which coincides with the negative impulse 52. The positive impulse 54is variable within a relatively narrow limit of approximately onehorizontal line of voltage wave 31 to allow a continuous shift of thetime axis origin of the pattern on the face of the cathode ray tube.This small, and therefore stable, shift afforded by the multivibrator25, together with the line-by-line shift provided by the delay circuit22, is all that is necessary to allow an oscillograph 29 such as the DuMont Type 248 to examine any part of any line in the television frameperiod if the oscillograph 29 is synchronized on the pulses 54.

Although this invention has been illustrated by a specific embodiment,changes may be made therein without departing from the scope of thefollowing claims.

What is claimed is:

1. An electrical circuit comprising a source of electrical impulses; agenerator of a sawtooth wave voltage, said generator being connected tosaid source and synchronized by said impulses; a bi-stable oscillatorconnected to said generator and triggered by said sawtooth voltage, theoutput voltage of said oscillator having a rectangu- Iar waveform, saidoscillator having an adjustable bias source to set the time oftriggering of said oscillator with respect to the starting time of saidsawtooth wave; a differentiating circuit connected to said oscillator todifferentiate said rectangular wave; a source of positive electricalimpulses; a gate circuit having one input circut connected to saidsecond source and a sec ond input circuit connected to saiddifferentiating circuit, said gate circuit being biased to have anoutput voltage signal only when a positive output signal from saiddifierentiating circuit coincides with a positive pulse from said secondsource; and a single-shot multivibrator connected to said gate circuitto be triggered by said output voltage therefrom, said multivibratorhaving a duty cycle adjustment.

2. An electrical circuit comprising a source of electrical impulses inwhich some of said impulses have a higher repetition rate and others ofsaid impulses have a lower repetition rate; an integrating circuitconnected to said source to separate said lower repetition rate impulsesfrom said higher repetition rate impulses; a triggering circuitconnected to said integrating circuit and synchronized by said lowerrepetition rate impulses; a generator of a sawtooth voltage waveconnected to said triggering circuit to be triggered thereby; anoscillator connected to said generator and triggered by said sawtoothwave, the output voltage of said oscillator having a rectangularwaveform, said oscillator having an adjustable bias source to set thetime of triggering thereof with respect to the starting time of saidsawtooth wave; a differentiating circuit connected to said oscillator todifferentiate said rectangular wave; an integrating circuit having oneinput circuit connected to said source of electrical impulsesv and asecond input circuit connected to said differentiating circuit, saidgate circuit being biased to have an output voltage signal only when oneof said impulses from said source coincides with a. positive pulse fromsaid differentiating circuit; and a single-shot multivibrator connectedto said gate circuit to be triggered by said output signal therefrom,said multivibrator comprising an adjustment to vary the duty cycle ofthe output pulse from said multivibrator over a. range of less than tenper cent.

ALTON LE ROY OLSON.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date Hoeppner et a1. Mar. 20, 1951 Kroft Dec. 25, 1951

